Ian Earley wore preemie clothes until he was 9 months old. During potty training and beyond, he was too small to get on the toilet. And he couldn't reach the sink to wash his hands until he was 6.

Ian has Russell-Silver syndrome (RSS), a form of primordial dwarfism that affects 1 in 100,000 babies, according to the National Institutes of Health.

Without growth-hormone treatment, boys will only reach an average height of about 5 feet 1 inch, and girls will only grow to about 4 feet 10 inches.

"Clothing is a huge challenge," mother Heather Earley of Libertyville, Ill. said, "This past summer, even at the age of 7, Ian could wear certain size 4T shorts. We have to buy him 6-slim jeans due to his height. But they still need to be cinched at the waist."

Ian was so tiny that he needed pillows and head insets in strollers and car seats. And well beyond infancy, Ian had to sit rear facing in the car seat because of the weight requirement.

In about 40 percent of the cases, Russell-Silver results from the abnormal regulation of certain genes that control growth. Severe long-standing placental insufficiency can also lead to severe intrauterine growth deficiency that resembles RSS.

Children such as Ian struggle not only with the mechanics of the physical world but with the social stigma that comes with being unusually small.

His mother, a divorced mother of two, fought to get the right diagnosis for her son, one that often eludes pediatricians. She writes about the challenges of living with the syndrome on her blog, Russell-Silver Advocate.

"This child has the most amazing charisma of anyone I have met in my life," Earley, 43, said. "He has friends all over the place. When he was 4 and looked like 2, all his friends wanted to pick him up like he was a baby. Even to this day, I want to pick him up, he's so cute and cuddly.

"But he knows he is different and knows he is small," she said. "He has some anger issues because his brother is only a year and a half older and three times his size. He is an adorable and loving child but he hates being different."

RSS, sometimes referred to as Thumbelina syndrome because of the fragile, doll-like stature of the children, is characterized by slow body growth, poor muscle tone and digestive problems, such as reflux and constipation.

Their heads, however, are unusually large, compared to the rest of the body.

"Try putting a 12-month shirt over a 3-year-old head," said Earley, half joking that she has considered approaching the Gap about clothing for special needs children like Ian.

Ian Earley, 3, with his older and bigger brother Alexander, who was 5.

Unlike dwarfism, where one segment of the body is smaller than the other, RSS is a different kind of short stature; it's perfectly proportionate.

Other than their size, "they pretty much look like other members of the family," said Dr. John Graham, director of clinical genetics and dymorphology at Cedars Sinai Medical Center in Los Angeles.

But the small children have diminished fat and glycogen storage and many cannot break down sugar.

"They are underweight, even as much as people try to over-feed them," he said. "They can go for long periods without eating."

RSS is a set of clinical features that results in severe prenatal onset growth deficiency that affects the body, but not the head.

In less than half of all cases, the condition begins shortly after conception.

RSS can be seen in identical twins, although it only affects one of the fetuses because twinning can disrupt the normal gene regulation. The association with twinning may not be identified because in 10 percent of identical twins, one twin dies early in gestation.

Increases in RSS can also be seen with the use of assisted reproduction techniques because the procedures can also disrupt gene regulation.

The syndrome is not inherited and there is no demonstrated cause in about half the cases, Graham said.

Many of the children suffer from bouts of hypoglycemia. Some have a tendency as adults to develop Type 2 diabetes.

"They are programmed [in the fetus] to grow and survive on much less nutrition than anyone else," Graham said. "Their metabolism is set to run on a leaner fuel mixture."

Graham estimates that the syndrome is under-diagnosed and as many as 1 in 10,000 children may have the condition.

Abbie King: 'Our Real-Life Thumbelina'

The British media reported this week the story of Abbie King, 2, who is so tiny that she wears newborn-sized clothes and specially shoes. Standing, she barely reaches the arm of the sofa.

Two-feet tall and weighing less than 14 pounds, she is not much larger than her dolls. She has never had a high-chair because she can't see over the tray and, for the same reason, she's never had a baby walker. Like Ian, Abbie gets lots of stares and questions.

"When I took her to the supermarket when she was a baby, everyone cooed over her and said she looked like a little doll, but they always asked if she was premature," her mother, Emma Smith, told Britain's Daily Mail newspaper.

"As she's got older, people have said, 'Your baby shouldn't be eating a sandwich,' or, 'It's cruel to make that baby walk.' But when I tell them how old she is, they usually look embarrassed."

Like others with RSS, Ian and Abbie have distinguishing features: triangular face, a prominent forehead, narrow chin, small jaw and a mouth with turned-down corners. They can also have a curving of the fifth finger. Some have asymmetric growth in parts of their body, such as the legs, or learning disabilities.

Heather Earley, who has a healthy son, Alexander, 9, said she knew something was wrong when she gave birth to her tiny baby.

"Alexander was almost 9 pounds on my 110-pound frame, but Ian was only 4 pounds and he looked like an alien. He had a big head and was only 16 inches long," she said. "His head circumference was in the 80th percentile and his body was below the third percentile."

Ian Earley as a 4-pound baby.

Although Alexander wolfed down 6 ounces of formula at a single feeding and was on baby food at three months, Ian could barely drink 2 ounces at a time until he was 9 months old.

Earley fought to get a diagnosis as her son failed to thrive. Ian's doctor accused Earley of not feeding Ian adequately.

Tests revealed Ian had RSS when he was 9 months old.

Like many others, Ian has a gastro-tube, which he calls his "mickey button," so nutrition can be pumped directly into his stomach at night while he sleeps.

"He has a hard time getting enough calories in his body," his mother said.

At 18 months, after being hospitalized for hypoglycemia, his parents decided to put him on growth hormone to help augment his growth.

Anecdotal experience suggests that the final heights of the treated kids should fall with 2 to 3 inches of their genetically predicted heights. Some can gain as many as 4 to 5 inches of height.

"Even when they have a condition that predisposes them to shortness, it's better to have tall parents," said Dr. Mitchell Geffner, a pediatric endocrinologist at Children's Hospital Los Angeles and professor of pediatrics at Keck School of Medicine at University of Southern California.

Although growth hormone is used for short stature children who are otherwise normal, "in this case, it's not cosmetic," he said.

Children with RSS can be treated as early as 2 and continue treatment for 10 years, Geffner. "Generally, it's true; starting early, you have more time to use it. You let it linger and they'll fall further away and have more ground to recover."

Growth hormone has been used for 50 years and it has been a synthetic form since 1985. "It has an amazingly safe record," he said.

Ian receives one injection a day at home. The side effects are rare and usually reversible.

Children with Russell-Silver Syndrome Judged Unfairly

But the biggest challenge is social.

"People are extremely judgmental," Earley said. "We as society talk about being big: 'Look how big you are,' 'What a big boy,' but Ian is not big and he never will be big.

"They have no clue how difficult it is. When you can't get a child to eat, it's very scary," she said. "You are responsible for that child, to love and nurture. ... It becomes emotionally exhausting."

And because the syndrome is so rare, children often go undiagnosed.

"It's unknown, even in the medical community," said Mary Andrews, founder and CEO of the Magic Foundation, which supports families with growth disorders. "Unfortunately, it's tough to diagnose."

But the good news is that many of these children can live normal lives.

The Magic Foundation supports families such as the Earleys with new research and connects them to other families for support.

"We make sure they know every resource available for the children," Andrews said. "When a family calls to say they have a child with Russell-Silver syndrome, we put them on the phone and refer them to a division consultant -- someone who has a child with Russell-Silver -- so they can talk one-on-one."

As for Ian, he is now 42 pounds and 3½ feet tall;- still in the fifth percentile for weight but in 40th percentile for height.

"Society, as a whole, needs to remember that they might look different but they are not," said Heather Earley, who has great hope for her son's future. "We all grow in our own time."